1. Field of the Invention
The present invention relates to a semiconductor device provided with a transistor including an oxide semiconductor film and a method for manufacturing the semiconductor device.
2. Description of the Related Art
Attention has been focused on a technique for forming a transistor with use of a semiconductor thin film formed over a substrate (the transistor is also referred to as a thin film transistor (TFT)). The transistor is applied to a wide range of electronic devices such as an integrated circuit (IC) or an image display device (display device). A silicon-based semiconductor material is widely known as a material for a semiconductor thin film applicable to a transistor. As another material, an oxide semiconductor has been attracting attention.
For example, a transistor including an oxide semiconductor containing indium (In), gallium (Ga), and zinc (Zn) as an active layer is disclosed (see Patent Document 1).
Further, a technique of improving carrier mobility by forming stacked oxide semiconductor layers has been disclosed (see Patent Documents 2 and 3).